An abnormality of vascular tone and vascular reactivity is common in essential hypertension. Most detailed studies in man have been performed on the easily accessible vascular beds of the extremities. While abnormalities of renal perfusion can clearly cause or contribute to the development of hypertension, little is known about renal vascular reactivity in the patients with essential hypertension. Sodium restriction and drugs influencing sodium and potassium balance are widely utilized in the treatment of patients with essential hypertension. We have documented the effects of varying sodium intake on renal vascular reactivity in normal man, but reactivity in essential and secondary hypertension requires investigation. An optimal index of vascular reactivity is provided by the intra-arterial infusion of vasoactive agents, as the dose may be sufficiently small that complicating systemic effects do not occur. We will utilize this route to administer graded doses of a number of specific antagonists to norepinephrine and angiotensin's vascular action, to assess their role, respectively, in maintaining the increase in renal vascular resistance and hypertension. The studies will be done during clinically indicated selective renal arteriography and assessment will be made with the xenon washout method and the selective arteriogram. The objective is to assess the determinants of renal vascular tone and vascular reactivity in normal man, the character of variations from normal in patients with hypertension of diverse etiology and the relationship of these abnormalities to the state of the renin-angiotensin and sympathetic nervous system. BIBLIOGRAPHIC REFERENCES: Hollenberg NK, Williams GH, Burger BM, Ishikawa I, Adams DF: Blockade and stimulation of renal, adrenal and vascular receptors for angiotensin II in normal man. J Clin Invest 57:39-46, 1976. Williams GH, Hollenberg NK: 1-Sar, 8-Ala angiotensin II's effect on renal, adrenal and vascular receptors in man: Its usefulness in screening for renal and adrenal diseases. In The Effects of Antihypertensive Therapy Symposium, Excerpta Medica Foundation, Amsterdam, 1976, in press.